One of the advantages of having so many telescopes that look at most of the sky is that if an astronomer finds something interesting, there is probably an image of it before it is officially discovered sitting in the data archives of other satellites that no one would have wanted to see. That’s certainly the case with our latest interstellar visitor, 3i/Atlas.
We previously reported that Vera Rubin’s 3i/Atlas was detected long before it was officially discovered, but now we find that a new paper dates back to early May.
The passing Exoplanet Survey Satellite (TESS) is not designed to find interstellar visitors. As its name suggests, it is designed to see stars (bright) and see exoplanets traversing in front of them. However, the data was data and Tess happened to be looking at a part of the sky that 3i/Atlas was supposed to be the beginning of this year, so Michigan’s Adina Feinstein and Darryl Seligman and Auburn’s John Noonan decided to see if they could find the data in the telescope archive.
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Until May 7, 2025, over the course of two separate observation periods, it turns out they can. Tess captures images every 200 seconds, and 3i/Atlas moves much faster than Tess is designed to see, so the team had to use a technique known as “Shift-Stacking.” They predicted where the interstellar objects (ISOs) would be in each image, shifted the photos to be in the same place in all photos, stacked multiple of photos, and otherwise obtained a clear signal of the objects to find in one image.
3i/Atlas began the observation period at about 6.35 Au by the end of the second window on June 2nd, moving to about 5.47 Au. During that time, the decrease in distance accounted for only an increase in brightness of about 1.5, but the flow increased five times.
Related: James Webb’s telescope image reveals that there is something strange in the interstellar comet 3i/atlas
There has already been a lot of speculation about the possibility that it is causing some of the more interesting features of 3i/Atlas, from data collection errors to the object itself, which is an alien technology. However, the authors have a much more common explanation of this seemingly strange event. The ISO may have been delving into “bisphere resistant” materials such as carbon dioxide and carbon monoxide. These have much higher sublimation points than water ice and can cause a significant increase in brightness, but most of our own solar system comets do not show the same dramatic increase in brightness far from the sun. For researchers, this is another data point that is likely that comets from other solar systems have a very different composition than those bound by us.
To find more differences, they also tried to see the period of nuclear rotation in the ISO. However, there was not a clear signal sufficient to describe whether the nucleus was actually moving. Perhaps this is caused by coma, which obscures notable features, making it difficult for Tess to detect changes in brightness caused by its rotation.
As we continue to study all the new interstellar objects we encounter in our paths, we begin to learn more and more about them. This paper will definitely come more as it will be added to that corpus of knowledge and will begin sifting through old data with all the telescopes that astronomers can find as they try to unlock the mysteries of our enigmatic visitors.
The original version of this article was published today in Universe.
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